Tank for electroanesthetizing fish

ABSTRACT

Anode and cathode electrodes are placed at the upstream and downstream ends of an elongated tank containing fish to be electroanesthetized by applying an electric signal to the electrodes to create an electric field within the tank sufficient to induce petit mal in the fish. By maintaining a flow of water in the tank from the end containing the anode electrode to this end containing the cathode electrode, the fish will tend to head toward the anode electrode and be subject to the largest voltage gradient induced by the electric field. A barrier at each of the anode and cathode electrodes prevents contact by the fish to protect the fish against injurious electrical shock.

CROSS REFERENCE TO RELATED APPLICATIONS

Circuitry useful in the practice of the present application is disclosedin my copending application entitled "ELECTROFISHING APPARATUS ANDMETHOD", Ser. No. 446,652, now U.S. Pat. No. 5,111,379. The circuitrydescribed therein is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to apparatus for electroanesthetizingaquatic animals and, more particularly, to a holding tank forelectroanesthetizing fish.

2. Description of Related Art

Since about the turn of the century, batches of fish have beenelectroanesthesized for both scientific and commercial purposes. Forscientific purposes, small tanks are used to contain a limited number offish. For commercial purposes, much larger tanks are used to permitelectroanesthetizing a large batch of fish commensurate with theproduction rate of the related commercial purposes. For each purpose, anelectric charge is introduced through electrodes disposed at the opposedends or opposed sides of the tank. A sufficient electrical charge isprovided to induce epileptic seizures in the fish. Two significantlevels of seizure are recognizable: petit mal and grand mal. In bothtypes of seizures, the fish lose consciousness and lack of motoractivity. In petit mal, the muscles of the fish become flaccid but ingrand mal, tetany occurs. Normally, the fish recover consciousnessalmost immediately after the electric charge is removed if the seizurewas limited to petit mal. In the event the seizure is grand mal,regaining consciousness is much more gradual.

In both types of seizures, the fish suffer apnea, whether it be a mildor severe loss of breathing. Such loss of breathing has seriousconsequences for the fish and it is essential that grand mal be avoided.Moreover, petit mal should not be prolonged beyond the minimum timerequired to maintain unconscious.

Epileptic seizures are always accompanied by severe muscle contractionsthat are capable of breaking bones and rupturing soft tissues attachedto muscle myotomes. These contractions are most commonly of a type knownas myoclonic jerks, which are a simultaneous contractions of pairedmyotomes on either side of the spine. This simultaneous andinstantaneous seizure of parallel muscles causes compression fracturesof the spine and actually crushing (longitudinally) of individual andgroups of vertebrae. Myoclonic jerks have an equal probability ofoccurrence in both petit mal and grand mal. When electroanesthesia isused for non aquatic animals (it has also been used for humans), it iscustomary to inject a muscle relaxing drug, such as curare (generallypresently banned) or succinyl choline chloride to prevent these damagingmuscle contractions from occurring.

More specifically, commercial fish processors of domestically raisedfish, such as catfish and trout, use electroanesthesia to stun the fishjust prior to processing for market. Typically, this stunning process iscrude. A large stainless steel basket filled with hundreds of pounds offish is hoisted from a holding tank. A steel rod is inserted into andalong the central axis of the basket and serves as a first electrode.The basket serves as a second electrode. Electric current is supplied toand flows between the two electrodes and the mass of intervening animaltissues until the fish are completely stunned. Thereafter, the fish aredumped on to moving belts and enter the processing rooms. Duringapplication of electric current, the fish suffer myoclonic jerks, havebroken backs and bleed internally. This bleeding, appearing in the formof hematomas, are present in the fish fillets sold.

When electroanesthesia is used for the study of various facets of fish,the damage resulting to the tissues and bone structure due to thepresently used electroanesthesia procedures prevents certain types ofstudies and may skew findings or analysis. For fish to be returned tothe body of water from where they were taken, such as fish on theendangered list, fatal injuries are unacceptable as well as injuriesaffecting reproduction, survivability and significant shortening of thelife span. Establishing petit mal by introduction of chemicals,including muscle relaxants, is difficult in the case of aquatic animalsand is discouraged, if not forbidden, by ecological and environmentalconsiderations.

SUMMARY OF THE INVENTION

A holding tank for electroanesthetizing fish has water flowing from oneend to the other and is of elongated configuration with a width close tothe length of the fish to be placed therein. An anode electrode islocated at the upstream end and a cathode electrode is located at thedownstream end. Upon applying an electric signal having a batch of highfrequency pulses repeated at a low frequency to the anode and cathodeelectrodes, the fish are induced to align themselves toward and swim tothe upstream end of the tank (electrotaxis). Such alignment permitsdetermination of the appropriate power level of the signal to inducepetit mal and prevent presence of grand mal. The accurate determinationof electrical power in combination with a specific pulse train toprevent myoclonic jerks anesthetizes the fish for either scientific orcommercial purposes without injury to the fish.

It is therefore a primary object of the present invention toelectroanesthetize aquatic animals without injuring them.

Another object of the present invention is to electroanesthetize fish toa petit mal state without inducing myoclonic jerks.

Yet another object of the present invention is to provide a holding tankfor electroanesthetizing fish without causing injury to the fish.

Yet another object of the present invention is to provide a holding tankfor electroanesthetizing fish, which tank is adaptable to the size ofthe fish contained therein.

A further object of the present invention is to provide apparatus forelectroanesthetizing fish which apparatus may be modified to accept anysize batch of any size fish.

A yet further object of the present invention is to provide a tank forelectroanesthetizing fish, which tank has fresh or recycled waterflowing therethrough.

A still further object of the present invention is to provide a methodfor electroanesthetizing aquatic animals without causing injury to them.

These and other objects of the present invention will become apparent tothose skilled in the art as the description thereof proceeds.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described with greater specificity andclarity with reference to the following drawings, in which:

FIG. 1 is a perspective view of a tank for electroanesthetizing fish;

FIG. 2 is a partial cross-sectional view taken along lines 2--2, asshown in FIG. 1;

FIG. 3 illustrates a detail for modifying the width of the tank;

FIG. 4 illustrates a detail for diffusing the water flow through thetank;

FIG. 5 is a top view of a variant tank;

FIG. 6 is a side view of the variant tank;

FIG. 7 is an elevational view of one of the electrodes;

FIG. 8 is a side view of the electrode shown in FIG. 7; and

FIG. 9 is a cross-sectional view taken along lines 9--9, as shown inFIG. 7.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, there is illustrated a tank 10 for inducingelectroanesthesia in fish. As will be described below, use of tank 10produces petit mal in fish without the muscle, bone and spinal injuriesresulting from presently used apparatus for inducing electroanesthesia.Furthermore, use of tank 10 eliminates the need for chemicals to renderfish unconscious and cause cessation of motor activity or musclerelaxant chemicals to reduce injuries during electroanesthesia. Bothtypes of chemicals may soon be banned because of their harmful effectsto endangered species; furthermore, poisoning or ill effects from eatingfish containing such chemicals is eliminated. Ecological andenvironmental impacts of such chemicals have caused or may cause them tobe banned.

Typically, the structure of tank 10 is of plastic, epoxy or otherelectrically non conductive material. The illustrated size, whether forscientific or commercial purposes, may be on the order to twelve feetlong by two feet wide by thirty inches deep. This size may vary,particularly the width, as a function of the size of the fish and thenumber of fish per batch to be electroanesthetized. The tank may includea cabinet 12 disposed at one end, which cabinet includes a pump fordrawing water from one end and injecting it at the other end to create aconstant water flow through the tank. The cabinet may also includecircuit unit 14 for generating and transmitting a particular electricalsignal between anode plate 16 and cathode plate 18. For example, thecircuitry may be of the type described in pending patent applicationentitled "ELECTROFISHING APPARATUS AND METHOD", Ser. No. 446,652. Such acircuit produces a signal having a packet of high frequency pulsesrepeated at a low frequency rate. Such pulses have several benefits.First, it is well known that fish in the presence of an electric fieldand under the influence of a rheobase voltage are involuntarily causedto head toward the anode electrode through an induced normal swimmingmuscular response (electrotaxis). This condition is augmented by theflow of water from anode plate 16 to cathode plate 18 since fish, evenwithout the presence of an electric field, tend to orient themselveswith their head into a water current. Knowing the average size of thefish within tank 10, a sufficient power level of the signal transmittedby circuit unit 14 is supplied to subject the fish to a voltage gradientfrom head to tail greater than the rheobase voltage, irrespective ofwhere within the tank the fish may be. Thus, all the fish within thetank will be under the influence of the electric field generatedsufficient to produce electrotaxis.

The electric field will produce petit mal in the fish, which is acondition in which the fish are unconscious and motor activity ceases.Myoclonic jerks, usually producing spinal and musculature injuries areavoided by the nature of the pulse train transmitted, which pulse trainpermits relaxation of the white tissue muscles between pulses andaccompanying red tissue muscle stimulations.

To obtain a relatively uniform flow rate laterally across tank 10, anupstream diffuser 20 may be used; such a diffuser may be a simpleapertured plate, as illustrated in FIGS. 1 and 2. A similar diffuserplate 22 may be used at the downstream end upstream of cathode plate 18to encourage relatively uniform flow rate laterally across the tank. Asparticularly shown in FIG. 2, a pump 30 includes an outlet pipe 32terminating in one or more outlets 34 in general proximity with anodeplate 16. For this purpose, the anode plate may be apertured, asindicated. Downstream of diffuser plate 22, a water pick-up inlet 34,which may include a filter 36, is connected to a conduit 38 to conveythe water to inlet 40 of pump 30. The operation of pump 30 is controlledby circuit unit 14.

The width and depth of tank 10 may be optimized for scientific orcommercial purposes where the size and number of fish per batch to beelectroanesthetized are known, as shown in FIG. 3. For more general use,side walls 50 and 56 and bottom 52 are fixed. The depth of the water inthe tank is regulated by controlling the amount of water introduced tothe tank. The effective width of the tank may be adjusted by positioninga moveable wall 54 closer to or further away from fixed side wall 56.Thus, the space between moveable wall 54 and side wall 50 and betweenwhich the fish are placed may be adjusted to a width approximately thatof the length of the fish to be placed within the tank. Such adjustmentmay be readily performed by providing a plurality of pegs 58,60 defininga number of columns in each of diffuser plates 22,20 for receiving andmaintaining moveable wall 54. That is, the moveable wall may be placedbetween adjacent pairs of pegs toward or away from fixed wall 56 totemporarily set the width of the portion of the tank between movablewall 54 and fixed wall 50 to receive the fish. Preferable, the lateraldimension of the tank should be just slightly greater than the length ofthe fish to encourage the fish to be aligned with the longitudinal axisof the tank. With the constant flow of water, the fish will tend to headupstream.

Diffuser plates 20 and 22 may be apertured, as illustrated in FIG. 1.Alternatively, the diffuser plates may be a diffuser means 66 supportinga plurality of fixed or positionable vanes 68 to direct the outflow fromoutlet(s) 34 of pump 30 generally uniformly across the width and heightof tank 10, as shown in FIG. 4. To maintain such uniformity of flow, thedownstream diffusion means would be similarly vaned to minimizelocations of non-waterflow or whirlpooling.

Means for draining tank 10 would also be provided, whether by a suctionpump or a simple outlet 70 having a valve 72 for controlling flowthrough exhaust conduit 74. Fill of the tank may be through aconventional pump drawing water from the body of water the fish camefrom. An other source of water may also be used.

For commercial purposes, the initial step in processing fish is usuallythat of electroanesthetizing the fish. For this reason, tank 10 may belocated in proximity to the source of the fish, whether a stream, theocean, or a feed pond. Moreover, the water flow in the tank may be waterdrawn from such stream, ocean or pond and returned thereto. To eliminatethe cost and complexities of attendant pumps for this purpose and if anadjacent stream is the source of the water, water upstream may bechanneled through the tank and evacuated downstream whereby gravityprovides the requisite impetus for flow and the rate of flow iscontrolled by gates or other valve elements.

A tank 100 suitable for this purpose is illustrated in FIGS. 5 and 6. Aninflow of water is provided through conduit 102, which inflow may be theoutflow from a pump or natural gravity induced flow from a source ofwater. Outflow is through conduit 104, which outflow may be induced by apump or by gravity. With such inflow and outflow, fish 106 in tank 100are continuously swimming in fresh water. The length, width and heightof tank 100 are, as described above, a function of the size and numberof fish per batch to be electroanesthetized. Accordingly, tank 100 mayinclude a moveable wall, such as described with respect to tank 10 orother means may be employed to reduce the width of tank 100 commensuratewith the size of the fish to obtain upstream orientation of the fish.Circuit unit 110 generates a pulse train of the type described above totransmit a stream of high frequency pulses repeated at a low frequencyrate from anode electrode 112 to cathode electrode 114 to establish anelectric field therebetween.

Because cost is always a consideration, the anode and cathode electrodesmay be constructed in accordance with the structure illustrated indetail in FIGS. 7, 8 and 9. Each electrode (112,114) includes upper andlower bars 116,118 interconnected by a plurality of single or pairedwires or rods 120. Bars 116,118 may be electrically conductive. However,if such bars are electrically conductive, there is a danger that thefish may come in direct contact with the bars and thereby be injured. Toavoid such injury, the bars may be electrically nonconductive and aconductor 122 may be disposed in each bar to electrically interconnectthe respective ends of conductors 120. One or both of conductors 122 areelectrically connected to electrical conductor 124. Conductor 124extending from anode electrode 112 and conductor 124 extending fromcathode electrode 114 are connected to the respective one of anode andcathode leads 126,128 extending from circuit unit 110.

To prevent contact by the fish with any of conductors 120 of the anodeor cathode electrodes a water permeable barrier or wall must be locatedabout the conductors. Such a barrier may be formed by plurality ofhollow apertured plastic balls of the type sold commercially as practicegolf balls, baseballs or softballs threaded upon each or upon pairs ofconductors (as illustrated). Balls of this type are sometimes referredto as "whiffle" balls or by the trademark "Fun Ball". These hollowapertured balls 130 prevent direct contact by the fish with the engagedconductor(s) yet the conductors remain essentially uninsulated from thesurrounding water resulting in minimal, if any, degradation of electricfield strength between the anode and cathode electrodes.

Water flowing through each of anode electrode 112 and cathode electrode114 will become turbulated because of the flow through and aroundapertured balls 130; moreover, the flow will be generally diffusedacross the full height and breadth of the anode electrode and thecathode electrode. Such flow diffusion downstream of anode electrode 112and maintained by cathode electrode 114 will tend to maintain areasonably uniform lateral cross-sectional flow rate in tank 110.Additionally, the essentially uniform arrangement of conductors 120across each of the upstream and downstream ends of tank 110 will providea relatively uniform field strength across the tank. It is to beunderstood that the flow rate across the tank, as well as the fieldstrength across the tank may be modified for special circumstances orfor special purposes by altering the position and number of conductorsalong with altering the size, water permeability and number of hollowballs 130.

By constructing the anode electrode and cathode electrode as shown inFIGS. 7, 8 and 9, it is possible to eliminate a diffuser plate (20, 22or 66) at both the upstream and downstream ends of the tank. That is,the anode electrode and cathode electrode perform the water flowdiffusing functions as well as the associated electrical fieldgenerating functions.

It is to be understood that tank 100 may incorporate moveable walls, asdescribed with respect to tank 10. Furthermore, a pump for recirculatingthe water in tank 100, like that shown for tank 10 may be employed.Alternatively, tank 10 may be used in circumstances of continuouslyreceiving fresh water and discharging water from the downstream end asdescribed with respect to tank 100. Anode electrode 112 and cathodeelectrode 114 may be used in tank 10 in place of the anode and cathodeand the diffuser plates shown in FIGS. 1-4.

While the principles of the invention have now been made clear in anillustrative embodiment, there will be immediately obvious to thoseskilled in the art many modifications of structure, arrangement,proportions, elements, materials and components used in the practice ofthe invention which are particularly adapted for specific environmentsand operating requirements without departing from those principles.

I claim:
 1. Apparatus for electroanesthetizing aquatic animals, saidapparatus comprising in combination:a) a tank for containing water andthe aquatic animals to be electroanesthetized; b) a source of electricpower for generating an electric signal to establish an electric fieldin said tank to electroanesthetize the aquatic animals; c) means forproducing a flow of water within said tank from an upstream end of saidtank to a downstream end of said tank; d) a first electrode disposed atthe upstream end of said tank; e) a second electrode disposed at thedownstream end of said tank; and f) means for interconnecting said firstand second electrodes with said power source to establish the electricfield and commensurate flow of electric current between said first andsecond electrodes.
 2. The apparatus as set forth in claim 1 includingmeans for altering the lateral cross-section of said tank to conform thewidth of the tank with the length of the aquatic animals.
 3. Theapparatus as set forth in claim 2 wherein said altering means includes amovable side wall for altering the effective width of said tankcontaining the aquatic animals.
 4. The apparatus as set forth in claim 1including means for shielding at least one of said first and secondelectrodes to prevent contact between the aquatic animals and the atleast one of said first and second electrodes.
 5. The apparatus as setforth in claim 4 wherein said shielding means includes further shieldingmeans for shielding the other of said first and second electrodes. 6.The apparatus as set forth in claim 5 wherein said further shieldingmeans comprises means for diffusing the flow of water through said tank.7. The apparatus as set forth in claim 4 wherein said shielding meanscomprises means for diffusing the flow of water through said tank. 8.The apparatus as set forth in claim 1 wherein said inducing meansincludes means for diffusing the flow of water through said tank.
 9. Theapparatus as set forth in claim 1 wherein the electric signal generatedby said power source comprises a pulse train having a packet of highfrequency pulses repeated at a low frequency rate for inducing petit malin the aquatic animals and for preventing myoclonic jerks in the aquaticanimals.
 10. The apparatus as set forth in claim 1 wherein said firstelectrode is an anode electrode and wherein said second electrode is acathode electrode.
 11. The apparatus as set forth in claim 10 whereinsaid tank includes means for inducing the aquatic animals to headupstream.
 12. The apparatus as set forth in claim 1 wherein each of saidfirst and second electrodes comprises an electrically conducting plate.13. The apparatus as set forth in claim 1 wherein each of said first andsecond electrodes comprises electrically interconnected rods.
 14. Theapparatus as set forth in claim 13 including means for shielding saidrods of at least one of said first and second electrodes against contactof said rods by said fish.
 15. The apparatus as set forth in claim 14wherein said shielding means comprises a barrier.
 16. The apparatus asset forth in claim 13 wherein said shielding means comprises a pluralityof apertured hollow spheres penetrably engaged by said rods. 17.Apparatus for inducing petit mal in aquatic animals without causinginjuries in the aquatic animals due to myoclonic jerks, said apparatuscomprising in combination:a) a tank for containing water and the aquaticanimals; b) means for producing a flow of water from one end of saidtank to the other end of said tank; c) an anode electrode disposed atsaid one end of said tank; d) a cathode electrode disposed at said otherend of said tank; e) a signal source for generating a pulse train havinga packet of high frequency pulses repeated at a low frequency rate toproduce an electric field within said tank; and f) means forinterconnecting said signal source with said anode and cathodeelectrodes.
 18. The apparatus as set forth in claim 17 including meansfor discouraging the aquatic animals to remain broadside to the flow ofwater.
 19. The apparatus as set forth in claim 17 wherein said signalsource generates an electric field of sufficient power to establish avoltage gradient across each aquatic animal at least equivalent to therheobase voltage of the respective aquatic animal.
 20. The apparatus asset forth in claim 19 including means for discouraging the aquaticanimals to remain broadside to the flow of water.
 21. The apparatus asset forth in claim 17 including means for shielding the aquatic animalsfrom said anode electrode to prevent contact between the aquatic animalsand said anode electrode.
 22. The apparatus as set forth in claim 17including means for producing an essentially uniform flow rate laterallyacross said tank.
 23. The apparatus as set forth in claim 22 whereinsaid producing means comprises means for shielding the aquatic animalsfrom said anode electrode to prevent contact between the aquatic animalsand said anode electrode.
 24. The apparatus as set forth in claim 23wherein said anode electrode comprises a plurality of rods and whereinsaid producing means comprises a plurality of apertured hollow spherespenetrably engaged by said rods.